This invention relates to optical components and methods for their manufacture.
Many optical components, such as optical waveguides, utilize diffractive and/or periodic structures. One example is a fiber Bragg grating (“FBG”), which has a periodic variation in index along its length to provide, for example, selective reflection of specific wavelengths. The periodic variation is typically on the order of the reflection wavelength. FBG devices have many potential uses in the established and emerging fields of optical communications and optical fiber sensing. For example, FBG's can be used for dispersion compensation and laser amplifier gain equalization.
A Bragg grating writer (“BGW”) is a system for imprinting the index variation for an FBG or similar optical waveguide device. Referring to FIG. 1, an example of a BGW geometry is one that relies on a phase mask 110 in near contact with an optical fiber 120. In some embodiments, phase mask 110 may be a transmission diffraction grating optimized for diffracting incident illumination into +1 and −1 orders. When illuminated with radiation 115 from an appropriate source, phase mask 110 generates an exposure pattern having a spatially-varying intensity on a photosensitive fiber core 140 of optical fiber 120. The refractive index of the photosensitive fiber core responds to the spatially-varying exposure pattern, resulting in a refractive index modulation having an amplitude typically of about 10−4 to 10−3.